1. Field of the Invention
The present invention relates to an optical connection device used in the field of optical communications and particularly relates to an optical connection device which can be integrated for optically coupling light beams propagated through optical waveguides to optical elements respectively.
2. Related Art
The quantity of information processed by an information processor such as a computer has been increasing steadily. In conjunction with this tendency, the number of wiring circuits inside or between electronic circuit boards used for forming the information processor has increased, and higher-density mounting of electronic circuits is required. However, problems such as interference of signals between wiring circuits and propagation delay caused by increase in wiring distance are growing more serious.
Public attention has been paid to optical connection technology as a means for solving these problems. The optical connection technology is suited to transmission or a large quantity of information because parallel mounting can be made without the problem of mutual interference in transmission of optical signals. Wiring circuits inside each electronic circuit board can be replaced by so-called optical circuits that transmit optical signals from light sources (light-emitting elements) mounted on the board to photo detectors (photodetecting elements) through optical transmission units such as optical waveguides.
The electronic circuits are however different from the optical circuits at a lot of points. In the optical circuits, it is necessary to connect optical elements and transmission paths such as optical waveguides to one another. Optical coupling, however, needs precise positioning (alignment) and is not easy compared with electric connection that can be effectuated by simple contact. Generally, in order to connect electronic devices to printed wiring circuits on an electronic circuit board, pins of the electronic devices are inserted into the printed wiring board and soldered to the printed wiring board. It would also be desirable that optical connection can be made by a simple method such as an inserting and fixing method as described above. Such a simple optical connection unit is now named “optical pin” for the pins of the electronic devices.
For example, there is known an optical pin that conducts optical connection by inserting an optical fiber into a hole that pierces an optical waveguide (see Proceedings of Optics Japan 2001, 6pD1). That is, an optical waveguide is formed in a board, and a through-hole is provided in the board so as to pierce the optical waveguide. A gradient index optical fiber having a tip processed so as to be inclined at an angle of 45° is inserted into the through-hole so that light propagated through the optical waveguide can be turned by 90°. The optical pin is configured so that the turned light is connected to an optoelectronic integrated circuit outside the optical waveguide by the lens function of the gradient index optical fiber
As disclosed in JP-A-7-86555, there is known a method in which photoactive elements such as semiconductor lasers or photodiodes, microlenses and prismatic V-grooves are used for propagating light in a free space by multiple reflection to thereby achieve an optoelectronic integrated circuit.
The diameter of the optical pin is however very small to be 127 μm because a gradient index optical fiber is used as the optical pin. For this reason, there is the drawback that the optical pin is easily broken, and that it is difficult to handle the optical pin during assembly. Meanwhile, since it is impossible to take the pin interval smaller than 250 μm, there is also a problem that such optical pins are unsuitable for integration.
In addition, tolerance in the processing position of each portion that combines with the optical waveguide is too strict to obtain good performance. In an optical sense, there is a problem that coupling characteristic deteriorates because astigmatic difference is produced in the horizontal direction of the optical waveguide by the lens function of the optical fiber after the optical path is turned.
Thus, the design of a light-condensing system of optical pins using optical fibers is limited variously.
On the other hand, in the case where light is propagated by multiple reflection in prisms, the dimensional tolerance of the prisms becomes strict because the profile accuracy of each prism surface exerts influence on the dimensional tolerance multistageously. It is also difficult to mount the prisms on an optoelectronic hybrid circuit board premised that the board is connected to optical fibers, because all optical systems provided are closed with optical path-turning systems respectively.